Radio access systems have been widely deployed to provide various types of communication services such as voice or data services. Radio access systems are generally multiple access systems in which available system resources (such as bandwidths and transmission power) are shared to support communication of multiple users. Examples of the multiple access systems include a code division multiple access (CDMA) system, a frequency division multiple access (FDMA) system, a time division multiple access (TDMA) system, an orthogonal frequency division multiple access (OFDMA) system, and a single carrier frequency division multiple access (SC-FDMA) system.